Migratory Orientation in the Indigo Bunting, Passerina cyanea: Part I: Evidence for Use of Celestial Cues

Abstract

The experimenat analysis of the orientation cues used by nocturnally migrating birds originated with Kramer's (1949) discovery that caged Blackcaps (Sylvia atricapilla) and Red-backed Shrikes( Lanius collurio) would, under certain conditions, spontaneously orient their migratory activity or Zugunruhe toward the portion of the cage corresponding to the normal migration direction of the species. These preliminary studies were extended by Sauer (1957, 1961) and Sauer and Sauer (1960) who tested the directional responses of three sylviid speciesp laced in cages under the natural night sky. The results indicated that some individuals consistently selected directions coincident with predicted migration routes; thus Sauer hypothesized that the birds were orienting by means of celestial cues. Additional experiments, performed under the artificial skies of a small planetarium, provided strong support for this idea.